Silica particles having carboxyl group and hydrophobic group, and composition for coating enamel wire

Abstract

The present invention addresses the problem of providing a silica sol in which silica particles are dispersed in a nitrogen-containing solvent and which is for mixing with a polyimide-based or polyamide-based polar resin with which the silica particles have good compatibility, and of providing an insulating resin composition in which the silica sol and the resin are combined, and an insulated and covered conductive wire which maintains high insulation life over a long period of time. Said problem is solved by means of a silica sol in which silica particles are dispersed in a nitrogen-containing solvent, wherein the silica particles have an average primary particle size of 5-100 nm, and the surfaces of at least a portion of the silica particles are coated with a hydrolysate of a carboxylic acid–based silane coupling agent (a) and a hydrolysate of a non-carboxylic acid–based silane coupling agent (b).

Description

Silica particles having carboxyl groups and hydrophobic groups, and composition for enameled wire coating

[0001] The present invention relates to a silica sol having a carboxyl group and a hydrophobic group dispersed in a nitrogen-containing solvent, an insulating resin composition using the same, and methods for producing the same.

[0002] A method has been disclosed in which hydroxyl groups on the surface of inorganic oxide particles such as silica react with alcohol to introduce alkoxysilyl groups, thereby organifying the particles and obtaining an inorganic oxide sol dispersed in an organic solvent such as toluene. In this method, phenyltrimethoxysilane is reacted with a methanol-dispersed silica sol, and the resulting silica sol is dispersed in a toluene solvent (see Patent Document 1).

[0003] Also disclosed is a silica sol obtained by solvent-substituting a methanol-dispersed silica sol with acetonitrile to obtain a silica sol dispersed in an acetonitrile-methanol mixed solvent, and then reacting the resulting silica sol with phenyltrimethoxysilane (see Patent Document 2).

[0004] Furthermore, a silica sol in which the surfaces of silica particles are modified with an aluminum compound has been disclosed (see Patent Document 3).

[0005] Also disclosed is an aluminum-containing silica sol dispersed in a nitrogen-containing solvent, and an insulating resin composition using the same (see Patent Document 4).

[0006] Japanese Patent Application Publication No. 2005-200294 International Publication No. 2009-008509 Pamphlet Japanese Patent Application Publication No. 2011-026183 International Publication No. 2022-097694 Pamphlet

[0007] The present invention provides a silica sol in which silica particles are dispersed in a nitrogen-containing solvent to achieve good compatibility with polyimide or polyamide polar resins. It also provides an insulating resin composition containing the silica sol and a resin. Furthermore, it provides an insulating coated conductor that, when coated with the insulating resin composition, can maintain a long insulation life.

[0008] The present invention provides, as a first aspect, a silica sol in which silica particles having an average primary particle size of 5 to 100 nm include silica particles whose particle surfaces are coated with a hydrolysate of a carboxylic acid silane coupling agent (a) and a hydrolysate of a non-carboxylic acid silane coupling agent (b), and the silica particles are dispersed in a nitrogen-containing solvent; as a second aspect, the silica sol according to the first aspect, in which the carboxylic acid silane coupling agent (a) is a silane coupling agent containing a carboxyl group, an acid anhydride group, a carboxylic acid ester group, or an organic group containing any of these; as a third aspect, the silica sol according to the first aspect or the second aspect, in which the non-carboxylic acid silane coupling agent (b) is a silane coupling agent containing an organic group containing at least an alkyl group, a (meth)acryloyl group, or an aryl group; and as a fourth aspect, the carboxylic acid silane coupling agent (a) is a silane coupling agent represented by Formula (1) and Formula (2): [Chemical 1] (In formulas (1) and (2), R １ and R ３ are each a carboxyl group, an acid anhydride group, a carboxylic acid ester group, or an organic group containing any of these, and are bonded to a silicon atom by a Si—C bond, and R ２ and R ４ each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group; X represents an alkylene group, an NH group, or an oxygen atom; a represents an integer of 1 to 3; b is an integer of 1 to 2; and c is an integer of 0 or 1. (In formula (3), R ５ are each an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, or a cyano group, and are bonded to a silicon atom by a Si—C bond, and R ６ represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, and d represents an integer of 1 to 3. In formulas (4) and (5), R ７and R ９ are each an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and bonded to a silicon atom by a Si—C bond, and R ８ and R １０ respectively represent an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group; Y represents an alkylene group, an NH group, or an oxygen atom; e represents an integer of 1 to 3; f represents an integer of 0 or 1; and g represents an integer of 1 to 3. (a) the organic solvent silica sol according to any one of the first to fourth aspects, which contains at least one silane compound selected from the group consisting of: (i) a carboxylic acid silane coupling agent (a) and a non-carboxylic acid silane coupling agent (b) and contains silica particles coated with a hydrolysate thereof in a mass ratio of 1:0.1 to 10; (ii) the silica sol according to any one of the first to sixth aspects, which contains the nitrogen-containing solvent as an amide solvent; (iii) the silica sol according to any one of the first to seventh aspects, which contains the nitrogen-containing solvent as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone; (iv) an insulating resin composition comprising the silica sol according to any one of the first to eighth aspects and a nitrogen-containing polymer; and (v) the composition according to the ninth aspect, in which the ratio of the nitrogen-containing polymer to 1 part by mass of silica contained in the silica sol is 1 to 100. As an eleventh aspect, the composition according to the ninth or tenth aspect, wherein the nitrogen-containing polymer is polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide; as a twelfth aspect, an insulated coated conductor that is insulated with the insulating resin composition according to any one of the ninth to eleventh aspects; as a thirteenth aspect, an insulating resin composition comprising a polyamic acid composed of 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) as a resin, and a resin / SiO mass ratio of 0.01 to 0.01; ２a silica-blended polyamic acid adjusted to a ratio of 0.1 to 0.25, and a silica-blended polyimide (A) having a thickness of 150 to 200 μm is baked on a Cu plate at 290° C. to obtain a Cu plate (coating thickness: 29 to 32 μm) having a dielectric breakdown life of 50 minutes or longer at a test temperature of 155° C. (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz; and a fourth aspect, the insulating resin composition according to the sixth aspect, wherein the insulating resin composition according to the seventh aspect is characterized in that the silica-blended polyamic acid (A) is adjusted to a ratio of 0.1 to 0.25, and a silica-blended polyimide (B) is baked on a Cu plate at 290° C. to obtain a silica-blended polyimide (B) having a thickness of 150 to 200 μm, and a silica-blended polyimide (C) having a thickness of 150 to 200 μm. and a fifteenth aspect, a method for producing an insulating resin composition, further comprising steps (E) and (F) in addition to steps (A) to (D) of the fourteenth aspect: step (E): a step (E) of mixing the silica sol obtained in step (D), in which silica particles are dispersed in a nitrogen-containing solvent, with a nitrogen-containing polymer; and step (F): a step of removing part or all of the nitrogen-containing solvent from the silica sol obtained in step (E).

[0009] Although overlapping with other descriptions, various aspects of the present invention are as follows. However, the present invention is not limited to the following. [1] A silica sol in which silica particles are dispersed in a nitrogen-containing solvent, the silica particles having an average primary particle diameter of 5 to 100 nm, and at least a portion of the silica particles are coated on their particle surfaces with a hydrolyzate of a carboxylic acid silane coupling agent (a) and a hydrolyzate of a non-carboxylic acid silane coupling agent (b). [2] The silica sol according to [1], in which the carboxylic acid silane coupling agent (a) is a silane coupling agent containing a carboxyl group, an acid anhydride group, a carboxylic acid ester group, or an organic group containing any of these. [3] The silica sol according to [1] or [2], in which the non-carboxylic acid silane coupling agent (b) is a silane coupling agent containing an organic group containing at least an alkyl group, a (meth)acryloyl group, or an aryl group. [4] The silica sol in which the carboxylic acid silane coupling agent (a) is a silane coupling agent containing a carboxylic acid silane coupling agent represented by formula (1) and formula (2): [Chemical 1] (In formulas (1) and (2), R １ and R ３ are each a carboxyl group, an acid anhydride group, a carboxylic acid ester group, or an organic group containing any of these, and are bonded to a silicon atom by a Si—C bond, and R ２ and R ４ [5] The silica sol according to any one of [1] to [3], wherein the non-carboxylic acid silane coupling agent (b) is a compound represented by the formula (3), the formula (4), or the formula (5): [Chemical Formula 2] (In formula (3), R ５ are each an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, or a cyano group, and are bonded to a silicon atom by a Si—C bond, and R ６represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, and d represents an integer of 1 to 3. In formulas (4) and (5), R ７ and R ９ are each an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and bonded to a silicon atom by a Si—C bond, and R ８ and R １０

[0023]

[0024] The silica sol according to any one of [1] to [4], which contains at least one silane compound selected from the group consisting of: (a) a carboxylic acid-based silane coupling agent; (b) a non-carboxylic acid-based silane coupling agent, and (b) a hydrolyzate thereof, in a mass ratio of 1:0.1 to 10.

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[10] The insulating resin composition according to [9], wherein the ratio of the mass parts of the nitrogen-containing polymer to 1 mass part of silica contained in the silica sol is 1 to 100.

[11] The insulating resin composition according to [9] or

[10] , wherein the nitrogen-containing polymer is polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide.

[12] An insulating coated conductor coated with the insulating resin composition according to any one of [9] to

[11] .

[13] An insulating coated conductor coated with the insulating resin composition according to any one of [9] to

[11] , wherein a polyamic acid composed of 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) is used as a resin, and the mass ratio of resin / SiO ２

[12] The insulating resin composition according to any one of [9] to

[11] , wherein a silica-blended polyamic acid adjusted to have a composition ratio of 85 / 15 is heated at 290°C on a Cu plate to bake a silica-blended polyimide onto the Cu plate (film thickness: 29 to 32 μm), and the insulating resin composition has a dielectric breakdown life of 50 minutes or more at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz.

[14] A method for producing a silica sol according to any one of [1] to [8], comprising the following steps (A) to (D): step (A): preparing a silica sol in which silica particles having an average primary particle diameter of 5 to 100 nm are dispersed in an aqueous medium; step (B): adding at least one carboxylic acid silane coupling agent (a) selected from the group consisting of formulas (1) and (2) to the silica sol obtained in step (A); step (C): performing solvent substitution on the dispersion medium of the silica sol obtained in step (B) with a nitrogen-containing solvent; and step (D): adding at least one non-carboxylic acid silane coupling agent (b) selected from the group consisting of formulas (3) to (5) to the silica sol obtained in step (C).

[15] A method for producing an insulating resin composition, further comprising the steps (E) and (F) of the steps (A) to (D) described in

[14] , further comprising the steps (E) and (F): mixing a nitrogen-containing polymer with the silica sol obtained in the step (D), in which silica particles are dispersed in a nitrogen-containing solvent; and (F) removing a part or all of the nitrogen-containing solvent from the silica sol obtained in the step (E).

[0010] The insulating resin obtained by coating and curing an insulating resin composition can contain silica particles to improve the insulation resistance of the substrate. The silica particles form a tight, strong coating layer with the insulating resin, protecting the substrate from electrical discharge-induced breakdown. Nitrogen-containing polymers with high insulating properties are often used as insulating resins. These nitrogen-containing polymers include, for example, polyimide, polyamide, polyamic acid, polyamideimide, polyetherimide, or polyesterimide. They are synthesized from diamines and acid anhydrides and have both polar moieties, such as an imide skeleton, carboxyl groups, or amide bonds, and hydrophobic moieties contained in the diamine or acid anhydride molecules. To form an insulating coating layer with good compatibility between resins having such structures and silica particles, it is necessary to impart similar properties to the silica particles. According to the present invention, a silica sol can be provided that can increase the affinity and dispersibility of silica particles in insulating resins to form a highly insulating coating layer.

[0011] To impart these properties, silica particles are coated with two types of silane compounds. One is to coat the silica particles with a silane compound (silane coupling agent) having a highly polar carboxyl group, and the other is to coat the silica particles with a silane compound (silane coupling agent) having a functional group other than a carboxyl group, particularly a highly hydrophobic silane compound (silane coupling agent). The carboxyl group-based partial structure formed on the silica particle surface forms a close interaction with the polar moiety of the nitrogen-containing polymer used as the insulating resin through hydrogen bonding or a covalent bond involving a reaction. Furthermore, the hydrophobic group, which is a functional group other than the carboxyl group formed on the silica particle surface, forms a close interaction with the hydrophobic moiety contained in the diamine molecule or acid anhydride molecule of the nitrogen-containing polymer used as the insulating resin through affinity. Because both functional groups on the silica particles can interact with the polar and hydrophobic moieties of the insulating resin, the insulating resin and silica particles can improve their adhesion to each other at the nanoscale between the surface-modified portions of the individual silica particles and the functional groups of the resin, which is thought to result in improved insulation resistance.

[0012] The present invention relates to silica particles having an average primary particle size of 5 to 100 nm, the surfaces of which are coated with a hydrolysate of a carboxylic acid silane coupling agent (a) and a hydrolysate of a non-carboxylic acid silane coupling agent (b), and a silica sol in which the silica particles are dispersed in a nitrogen-containing solvent. Alternatively, the present invention relates to a silica sol in which silica particles are dispersed in a nitrogen-containing solvent, the silica particles having an average primary particle size of 5 to 100 nm, and at least a portion of the silica particles are coated on their surfaces with a hydrolysate of a carboxylic acid silane coupling agent (a) and a hydrolysate of a non-carboxylic acid silane coupling agent (b).

[0013] The silica particles contained in the silica sol of the present invention have an average primary particle diameter of 5 to 100 nm, 10 to 70 nm, or 10 to 50 nm. The average primary particle diameter of the silica particles can be determined by the particle diameter (nm) measured by the nitrogen gas adsorption method (BET method). The particle diameter (average primary particle diameter D (nm)) measured by the nitrogen gas adsorption method (BET method) can be calculated by the specific surface area S (m ２ / g) and density ρ (g / cm ３ ), it is given by the formula D (nm) = 6000 / ρ × S. In the present invention, the density ρ of the silica particles is 2.2 (g / cm ３ ) was used.

[0014] Furthermore, the silica particles contained in the silica sol of the present invention have good dispersibility in nitrogen-containing solvents, and exhibit a particle size in the range of 5 to 100 nm, or 10 to 70 nm, as measured by dynamic light scattering (DLS) in a nitrogen-containing solvent.

[0015] The nitrogen-containing solvent used in the present invention has a functional group containing at least a nitrogen atom (nitrogen-containing functional group). Examples of the nitrogen-containing functional group include an amino group, a nitro group, and a cyano group. The nitrogen-containing solvent used in the present invention is preferably an amide-based solvent in which a nitrogen-containing functional group and a carbonyl group exist in one solvent molecule, and examples of the nitrogen-containing solvent include a chain structure and a cyclic structure. Examples of the nitrogen-containing functional group include an amino group, a nitro group, and a cyano group, but it is preferable to use an amino group. The amino group and the carbonyl group can be adjacent to each other or can exist via a carbon atom, and can be used, for example, as an amide bond, and amide-based solvents are preferably used.

[0016] Specific examples of nitrogen-containing solvents include dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, hexamethylphosphoric triamide, dimethylacrylamide, acryloylmorpholine, hydroxyethylacrylamide, isopropylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, dimethylaminopropylacrylamide methyl chloride quaternary salt, and dimethylaminoethyl acrylate benzyl chloride quaternary salt.

[0017] Preferred examples of nitrogen-containing solvents include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and N-ethylpyrrolidone.

[0018] In the present invention, the nitrogen-containing solvent may contain other solvents as long as the effect is not impaired.

[0019] That is, the nitrogen-containing solvent may be contained in an amount of 50 to 100% by volume, 90 to 100% by volume, 98 to 100% by volume, or 99 to 100% by volume of the total solvent, and other solvents may be contained in an amount of 0 to less than 50% by volume, 0 to less than 10% by volume, 0 to less than 2% by volume, or 0 to less than 1% by volume.

[0020] Other solvents include water, ketone-based solvents, ester-based solvents, alcohol-based solvents, glycol ether-based solvents, hydrocarbon-based solvents, halogen-based solvents, ether-based solvents, glycol-based solvents, and amine-based solvents.

[0021] For example, ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, etc.; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, etc.; alcohol-based solvents such as methanol, ethanol, isopropanol, benzyl alcohol, etc.; glycol ether-based solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, etc.; hydrocarbon-based solvents such as benzene, toluene, xylene, n-hexane, cyclohexane, etc.; halogen-based solvents such as dichloromethane, trichloroethylene, perchloroethylene, etc.; ether-based solvents such as dioxane, diethyl ether, tetrahydrofuran, etc.; glycol-based solvents such as ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, etc.; and amine-based solvents such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-methylethanolamine, 2-amino-2-methyl-1-propanol, etc.

[0022] In the present invention, as the carboxylic acid-based silane coupling agent (a), a silane coupling agent containing a carboxyl group, an acid anhydride group, a carboxylic acid ester group, or an organic group containing any of these can be used. These functional groups can be present in a ratio of 1 to 3 per molecule of the silane coupling agent. The organic group connected to the functional group of the carboxyl group, the acid anhydride group, or the carboxylic acid ester group can be an aliphatic structure, an aromatic structure, or a combination thereof. The aliphatic structure can be a saturated or unsaturated structure, and an alkyl group or an alkenyl group can be used.

[0023] The carboxylic acid-based silane coupling agent (a) can be at least one silane compound selected from the group consisting of formulas (1) and (2). In formulas (1) and (2), R １ and R ３ are each a carboxyl group, an acid anhydride group, a carboxylic acid ester group, or an organic group containing any of these, and are bonded to a silicon atom by a Si—C bond, and R ２ and R ４ each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group; X represents an alkylene group, an NH group, or an oxygen atom; a represents an integer of 1 to 3; b represents an integer of 1 or 2; and c represents an integer of 0 or 1.

[0024] Examples of silane coupling agents containing an organic group containing a carboxyl group include compounds of formula (1-1) in which two carboxyl group structures are bonded to a tetrahydroxydisiloxane skeleton, and products such as X-12-1135, a product of Shin-Etsu Chemical Co., Ltd., can be used.

[0025] Examples of silane coupling agents containing an organic group containing an acid anhydride group include those having an alkylene chain having 1 to 10 or 3 to 5 carbon atoms between the acid anhydride structure and the alkoxysilyl group, and silane coupling agents having a succinic anhydride structure can be used. For example, 3-trimethoxysilylpropylsuccinic anhydride can be used, and the product name X-12-967C, manufactured by Shin-Etsu Chemical Co., Ltd., represented by formula (1-2), can be used.

[0026] Silane coupling agents containing an organic group containing a carboxylic acid ester group include alkyl esters, aryl esters, and arylalkyl esters in the ester moiety. For example, alkyl groups include linear or branched alkyl groups having 1 to 10 carbon atoms and aryl groups having 6 to 40 carbon atoms. Arylalkyl groups include structures in which an alkylene group having 1 to 10 carbon atoms is bonded to an aryl group having 6 to 40 carbon atoms. Examples of the structure of these ester moieties include a methyl carboxylate structure, a t-butyl carboxylate structure, and a benzyl carboxylate structure. Furthermore, the carboxylic acid ester moiety and the alkoxysilyl group are connected by an alkylene group, and examples thereof include alkylene groups having 1 to 10 carbon atoms, which may contain a heteroatom. Examples of heteroatoms include nitrogen atoms and oxygen atoms, such as an NH group and an O group. The carboxylic acid ester moiety undergoes hydrolysis to form a carboxylic acid, and if the heteroatom contains a nitrogen atom, it becomes an amino acid, and the organic group containing a carboxylic acid ester group can be used as an amino acid generator. For example, the product represented by formula (1-3), product name X-88-475, manufactured by Shin-Etsu Chemical Co., Ltd., can be used.

[0027] In the present invention, the non-carboxylic acid silane coupling agent (b) refers to a silane coupling agent having a structure other than a carboxyl group. The non-carboxylic acid silane coupling agent (b) can be a silane coupling agent containing an organic group containing at least an alkyl group, a (meth)acryloyl group, or an aryl group. As long as the non-carboxylic acid silane coupling agent (b) contains an alkyl group, a (meth)acryloyl group, or an aryl group, it may also contain a functional group other than a carboxyl group. Examples of such functional groups include an alkenyl group, an epoxy group, a mercapto group, an amino group, a ureido group, or a cyano group.

[0028] In the present invention, the non-carboxylic acid silane coupling agent (b) contains at least one silane compound selected from the group consisting of formulas (3), (4), and (5).

[0029] In formula (3), R ５are each an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, or a cyano group, and are bonded to a silicon atom by a Si—C bond, and R ６ represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, and d represents an integer of 1 to 3. In formulas (4) and (5), R ７ and R ９ are each an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and bonded to a silicon atom by a Si—C bond, and R ８ and R １０ respectively represent an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group; Y represents an alkylene group, an NH group, or an oxygen atom; e represents an integer of 1 to 3; f represents an integer of 0 or 1; and g represents an integer of 1 to 3.

[0030] The alkyl group is an alkyl group having 1 to 18 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a cyclopropyl group, an n-butyl group, an i-butyl group, an s-butyl group, a t-butyl group, a cyclobutyl group, a 1-methyl-cyclopropyl group, a 2-methyl-cyclopropyl group, an n-pentyl group, a 1-methyl-n-butyl group, a 2-methyl-n-butyl group, a 3-methyl-n-butyl group, a 1,1-dimethyl-n-propyl group, a 1,2-dimethyl-n-propyl group, a 2,2-dimethyl-n-propyl group, a 1-ethyl- n-propyl group, cyclopentyl group, 1-methyl-cyclobutyl group, 2-methyl-cyclobutyl group, 3-methyl-cyclobutyl group, 1,2-dimethyl-cyclopropyl group, 2,3-dimethyl-cyclopropyl group, 1-ethyl-cyclopropyl group, 2-ethyl-cyclopropyl group, n-hexyl group, 1-methyl-n-pentyl group, 2-methyl-n-pentyl group, 3-methyl-n-pentyl group, 4-methyl-n-pentyl group, 1,1-dimethyl-n-butyl group, 1,2-dimethyl-n-butyl group, 1,3-dimethyl-n-butyl group , 2,2-dimethyl-n-butyl group, 2,3-dimethyl-n-butyl group, 3,3-dimethyl-n-butyl group, 1-ethyl-n-butyl group, 2-ethyl-n-butyl group, 1,1,2-trimethyl-n-propyl group, 1,2,2-trimethyl-n-propyl group, 1-ethyl-1-methyl-n-propyl group, 1-ethyl-2-methyl-n-propyl group, cyclohexyl group, 1-methyl-cyclopentyl group, 2-methyl-cyclopentyl group, 3-methyl-cyclopentyl group, 1-ethyl-cyclobutyl group, 2-ethyl-cyclobutyl group group, 3-ethyl-cyclobutyl group, 1,2-dimethyl-cyclobutyl group, 1,3-dimethyl-cyclobutyl group, 2,2-dimethyl-cyclobutyl group, 2,3-dimethyl-cyclobutyl group, 2,4-dimethyl-cyclobutyl group, 3,3-dimethyl-cyclobutyl group, 1-n-propyl-cyclopropyl group, 2-n-propyl-cyclopropyl group, 1-i-propyl-cyclopropyl group, 2-i-propyl-cyclopropyl group, 1,2,2-trimethyl-cyclopropyl group, 1,2,3-trimethyl-cyclopropyl group, 2,2,Examples include, but are not limited to, 3-trimethyl-cyclopropyl group, 1-ethyl-2-methyl-cyclopropyl group, 2-ethyl-1-methyl-cyclopropyl group, 2-ethyl-2-methyl-cyclopropyl group, 2-ethyl-3-methyl-cyclopropyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, and the like.

[0031] Furthermore, examples of the alkylene group include alkylene groups derived from the above-mentioned alkyl groups.

[0032] The aryl group is an aryl group having 6 to 30 carbon atoms, and examples thereof include a phenyl group, a naphthyl group, an anthracene group, and a pyrene group.

[0033] The alkenyl group is an alkenyl group having 2 to 10 carbon atoms, and examples thereof include ethenyl, 1-propenyl, 2-propenyl, 1-methyl-1-ethenyl, 1-butenyl, 2-butenyl, 3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylethenyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-n-propylethenyl, 1-methyl-1-butenyl, 1-methyl-2-butenyl, 1-methyl-3-butenyl, 2-ethyl-2-propenyl, 2-methyl-1-butenyl, 2-methyl-2-butenyl, 2-methyl-3-butenyl, 3 ...2-butenyl, 1-methyl-3-butenyl, 2-methyl-2-propenyl, 2-methyl-3-butenyl, 3-n-propylethenyl, 1-methyl-1-butenyl, 1-methyl-2-butenyl, 1-methyl-3-butenyl, 2-methyl-2-propenyl, 2-methyl-3-butenyl, 3-n-propylethenyl, 1-methyl-2-butenyl, 1-methyl-3-butenyl, 2-methyl-2-butenyl, 2-methyl-3-butenyl, 3-n-propylethenyl Examples of alkyl groups include, but are not limited to, 1-methyl-1-butenyl group, 3-methyl-2-butenyl group, 3-methyl-3-butenyl group, 1,1-dimethyl-2-propenyl group, 1-i-propylethenyl group, 1,2-dimethyl-1-propenyl group, 1,2-dimethyl-2-propenyl group, 1-cyclopentenyl group, 2-cyclopentenyl group, 3-cyclopentenyl group, 1-hexenyl group, 2-hexenyl group, 3-hexenyl group, 4-hexenyl group, 5-hexenyl group, 1-methyl-1-pentenyl group, 1-methyl-2-pentenyl group, 1-methyl-3-pentenyl group, 1-methyl-4-pentenyl group, 1-n-butylethenyl group, 2-methyl-1-pentenyl group, and 2-methyl-2-pentenyl group.

[0034] The alkoxy group includes alkoxy groups having 1 to 10 carbon atoms, such as methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, n-pentyloxy, 1-methyl-n-butoxy, 2-methyl-n-butoxy, 3-methyl-n-butoxy, 1,1-dimethyl-n-propoxy, 1,2-dimethyl-n-propoxy, 2,2-dimethyl-n-propoxy, 1-ethyl-n-propoxy, and n-hexyloxy, but is not limited to these.

[0035] The acyloxy group includes acyloxy groups having 2 to 10 carbon atoms, such as a methylcarbonyloxy group, an ethylcarbonyloxy group, an n-propylcarbonyloxy group, an i-propylcarbonyloxy group, an n-butylcarbonyloxy group, an i-butylcarbonyloxy group, an s-butylcarbonyloxy group, a t-butylcarbonyloxy group, an n-pentylcarbonyloxy group, a 1-methyl-n-butylcarbonyloxy group, a 2-methyl-n-butylcarbonyloxy group, a 3-methyl-n-butylcarbonyloxy group, a 1,1-dimethyl-n-propylcarbonyloxy group, a 1,2-dimethyl-n-propylcarbonyloxy group, a 2,2-dimethyl-n-propylcarbonyloxy group, a 1-ethyl-n-propylcarbonyloxy group, an n-hexylcarbonyloxy group, a 1-methyl-n-pentylcarbonyloxy group, and a 2-methyl-n-pentylcarbonyloxy group, but is not limited to these.

[0036] The halogen group includes fluorine, chlorine, bromine, iodine, and the like.

[0037] The (meth)acryloyl group refers to both an acryloyl group and a methacryloyl group. Examples of organic groups having a (meth)acryloyl group include a 3-methacryloxypropyl group and a 3-acryloxypropyl group.

[0038] An example of the organic group having a mercapto group is a 3-mercaptopropyl group.

[0039] Examples of organic groups having an amino group include a 2-aminoethyl group, a 3-aminopropyl group, an N-2-(aminoethyl)-3-aminopropyl group, an N-(1,3-dimethyl-butylidene)aminopropyl group, an N-phenyl-3-aminopropyl group, and an N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl group.

[0040] An example of the organic group having a ureido group is a 3-ureidopropyl group.

[0041] An example of the organic group having a cyano group is a 3-cyanopropyl group.

[0042] The compounds represented by the formulas (4) and (5) are preferably compounds capable of forming trimethylsilyl groups on the surface of silica particles.

[0043] Examples of such compounds include the following.

[0044] In the above formula, R １２ is an alkoxy group, such as a methoxy group or an ethoxy group. As the silane compound, a silane compound manufactured by Shin-Etsu Chemical Co., Ltd. can be used.

[0045] The silane compound reacts with hydroxyl groups, such as silanol groups, present on the surface of the silica particles to form siloxane bonds, thereby coating the surface of the silica particles with the silane compound. The reaction between the silane compound and the hydroxyl groups can be carried out at a temperature ranging from 20°C to the boiling point of the dispersion medium, for example, 20°C to 100°C. The reaction time is approximately 0.1 to 6 hours.

[0046] In the present invention, the total amount of the silane compound consisting of the carboxylic acid-based silane coupling agent (a) and the non-carboxylic acid-based silane coupling agent (b) for coating the surface of the silica particles is determined so that the number of silicon atoms in the silane compound is 0.4 / nm as the coating amount on the surface of the silica particles. ２ ~5.0 pieces / nm ２ The amount of coating can be set to correspond to the amount of coating.

[0047] The amount of the carboxylic acid-based silane coupling agent (a) added is determined so that the number of silicon atoms in the silane compound of the carboxylic acid-based silane coupling agent (a) is 0.1 / nm ２ ~3.0 pieces / nm ２ The amount of coating can be set to correspond to the amount of coating.

[0048] The amount of the non-carboxylic acid silane coupling agent (b) added is determined so that the number of silicon atoms in the silane compound of the non-carboxylic acid silane coupling agent (b) is 0.3 / nm ２ ~4.0 pieces / nm ２ The amount of coating can be set to correspond to the amount of coating.

[0049] Silica particles coated with the hydrolyzate of the carboxylic acid silane coupling agent (a):non-carboxylic acid silane coupling agent (b) can be obtained at a mass ratio of 1:0.1 to 10.

[0050] Water is required for the hydrolysis of the silane compound, and if the sol is an aqueous solvent, that aqueous solvent can be used. When the aqueous medium is replaced with an organic solvent such as methanol or ethanol, the water remaining in the solvent can be used. For example, water present in an amount of 0.01 to 4% by mass can be used. Furthermore, the hydrolysis can be carried out with or without a catalyst.

[0051] When the hydrolysis is performed without a catalyst, the silica particle surface is on the acidic side. When a catalyst is used, examples of the hydrolysis catalyst include metal chelate compounds, organic acids, inorganic acids, organic bases, and inorganic bases. Examples of metal chelate compounds used as hydrolysis catalysts include triethoxy mono(acetylacetonato)titanium and triethoxy mono(acetylacetonato)zirconium. Examples of organic acids used as hydrolysis catalysts include acetic acid and oxalic acid. Examples of inorganic acids used as hydrolysis catalysts include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid. Examples of organic bases used as hydrolysis catalysts include pyridine, pyrrole, piperazine, and quaternary ammonium salts. Examples of inorganic bases used as hydrolysis catalysts include ammonia, sodium hydroxide, and potassium hydroxide.

[0052] The silica sol of the present invention can be produced by a method comprising the following steps (A) to (D): step (A): preparing a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in an aqueous medium; step (B): adding at least one carboxylic acid-based silane coupling agent (a) selected from the group consisting of formulas (1) and (2) to the silica sol obtained in step (A); step (C): performing solvent substitution on the dispersion medium of the silica sol obtained in step (B) with a nitrogen-containing solvent; and step (D): adding at least one non-carboxylic acid-based silane coupling agent (b) selected from the group consisting of formulas (3) to (5) to the silica sol obtained in step (C).

[0053] The silica sol used in step (A) is preferably an acidic aqueous silica sol having a pH of 1.0 to 7.0, preferably 2.0 to 5.0. ２ The concentration is preferably in the range of 0.1 to 50% by mass, or 10 to 40% by mass.

[0054] In step (B), a carboxylic acid-based silane coupling agent (a) represented by formula (1) is added to the silica sol obtained in step (A), and the silica particle surfaces are coated with a hydrolyzate of the silane coupling agent of formula (1). Step (B) can be carried out at 50 to 100°C or 60 to 90°C for 0.1 to 10 hours. This reaction causes the hydrolyzate of the silane coupling agent of formula (1) to react with the silica particle surfaces, forming siloxane bonds. This reaction is preferably carried out at a pH in the acidic range described above; if carried out in an alkaline range, the carboxylic acid-based silane coupling agent of formula (1) may oligomerize, resulting in a reduced amount of coating on the silica particles.

[0055] When the carboxylic acid-based silane coupling agent of formula (1) has an acid anhydride group, two carboxyl groups can be generated by hydrolysis of part or all of the acid anhydride group. Also, when the carboxylic acid-based silane coupling agent of formula (1) has a carboxylic acid ester group, a carboxyl group is generated by hydrolysis.

[0056] In step (C), the dispersion medium of the silica sol obtained in step (B) is replaced with a nitrogen-containing solvent. The nitrogen-containing solvent is preferably an amide solvent, such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone. In the solvent replacement with a nitrogen-containing solvent, the water content can be adjusted to a range of 0.1 to 4.0% by mass, 1.0 to 2.5% by mass, or 1.5 to 2.0% by mass of the total solvent.

[0057] In step (D), at least one non-carboxylic acid silane coupling agent (b) selected from the group consisting of formulas (3) to (5) can be added to the silica sol obtained in step (C). In step (D), the non-carboxylic acid silane coupling agent (b) contains a hydrophobic silane coupling agent, and thus, by solvent substitution from the aqueous silica sol to a nitrogen-containing solvent silica sol, the hydrolyzate of the non-carboxylic acid silane coupling agent (b) reacts to form siloxane bonds. Step (D) can be carried out at 50 to 100°C or 60 to 90°C for 0.1 to 10 hours. This reaction causes the hydrolyzate of the silane coupling agent of formula (1) to react with the silica particle surface to form siloxane bonds.

[0058] The silica sol of the present invention in which silica particles are dispersed in a nitrogen-containing solvent can be combined with a nitrogen-containing polymer to obtain an insulating resin composition (resin varnish).

[0059] The insulating resin composition (resin varnish) can be produced by a method that further includes steps (E) and (F) in addition to steps (A) to (D): step (E): mixing the silica sol obtained in step (D), in which silica particles are dispersed in a nitrogen-containing solvent, with a nitrogen-containing polymer; and step (F): removing part or all of the nitrogen-containing solvent from the silica sol obtained in step (E).

[0060] The nitrogen-containing polymer may be blended in a ratio of 1 to 100 parts by mass per part by mass of silica contained in the silica sol.

[0061] The nitrogen-containing polymer may be a polyimide, a polyamide, a polyamic acid, a polyamideimide, a polyetherimide, or a polyesterimide.

[0062] The insulating resin composition can be applied to a conductor that requires insulation and then heated and cured at a temperature at which the solvent evaporates, forming an insulating film on the surface of the conductor. The heating temperature for removing the solvent is determined by the temperature and pressure, but is about 150°C to 300°C at normal pressure, or about 150°C to 400°C for imidization of the resin.

[0063] The conductor is a metal wire, particularly a copper wire, which is coated with enamel to form an electric wire and is used in industrial and domestic motors, transformers, coils, etc.

[0064] The insulating resin composition of the present invention can be used to produce an insulated coated conductor wire by coating an enamel-coated copper wire or by directly coating a copper wire with the insulating resin composition instead of enamel.

[0065] The insulating resin composition is obtained by mixing 1 part by mass of silica contained in silica sol with 1 to 100, 1 to 50, or 1 to 10 parts by mass of nitrogen-containing polymer.

[0066] The insulating resin composition can be applied to a conductor that requires insulation and then heated and cured at a temperature at which the solvent evaporates, forming an insulating film on the surface of the conductor. The heating temperature for removing the solvent is determined by the temperature and pressure, but is about 150°C to 300°C at normal pressure, or about 150°C to 400°C for imidization of the resin.

[0067] The insulating resin composition can be obtained by mixing and stirring the silica sol and the polymer with a mixer or disperser. Additives can be added to the mixture as desired.

[0068] A conductor coated with the insulating resin composition of the present invention has insulating properties and flexibility.

[0069] Flexibility is measured in accordance with JIS C 3216-3, Section 5. The insulated coated conductor of the present invention preferably has an insulating coating layer made of an insulating resin composition with a thickness of 35 μm and a silica concentration of 20% by mass, and the insulating coating layer has a flexibility of 1d to 2d. The flexibility is measured by determining the minimum winding diameter d at which cracks do not occur in the insulating coating of an insulated coated conductor stretched 20% compared to an insulated coated conductor stretched at no stretch, and is measured within the range from the original diameter (1d) to n times the original diameter (nd).

[0070] A polyamic acid consisting of 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) was used as the resin, and the mass ratio of resin / SiO ２ A silica-blended polyamic acid adjusted to a ratio of 85 / 15 is heated at 290°C on a Cu plate to obtain a Cu plate (coating thickness: 29 to 32 µm) on which a silica-blended polyimide is baked, and an insulating resin composition is obtained having a dielectric breakdown life of 50 minutes or more, or 50 to 1000 minutes, or 60 to 500 minutes, or 60 to 200 minutes at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz.

[0071] The present invention will be specifically described below by showing examples, but the present invention is not limited to the following examples in any sense.

[0072] [SiO ２ Measurement of Concentration] The silica sol was placed in a crucible and dried at 150°C, and the resulting gel was then fired at 1000°C, and the firing residue was weighed to calculate the concentration.

[0073] [Measurement of average primary particle diameter (particle diameter by nitrogen adsorption method)] The specific surface area of ​​the powder obtained by drying the acidic silica sol at 300°C was measured using a specific surface area measuring device Monosorb (trade name) MS-16 (manufactured by Yuasa Ionics Co., Ltd.).

[0074] [Measurement of Water Content] The water content was determined by Karl Fischer titration.

[0075] [pH Measurement] Measurement was carried out at 20°C using a pH meter (manufactured by DKK Toa Corporation).

[0076] [Measurement of Viscosity] The viscosity of the silica sol was measured using an Ostwald viscometer at 20° C. In the examples, the converted viscosity measured at 20° C. using a B-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd.) is shown in parentheses.

[0077] [Measurement of particle size by dynamic light scattering] Measurement was carried out using a dynamic light scattering particle size (DLS) measuring device (manufactured by Malvern Instruments, trade name: Zetasizer Nano).

[0078] [Solid content of polyamic acid] The polyamic acid was placed in an aluminum cup and baked at 200°C, and the baking residue was weighed and calculated.

[0079] Example 1 (A) Step: Water-dispersed silica sol ST-O-33 (average primary particle size 12 nm, pH 3, silica concentration 33 mass%, manufactured by Nissan Chemical Industries, Ltd.) was prepared. (B) Step: 1000 g of water-dispersed silica sol ST-O-33 (average primary particle size 12 nm, pH 3, silica concentration 33 mass%, manufactured by Nissan Chemical Industries, Ltd.) was charged into a 2 L recovery flask, and while stirring the sol with a magnetic stirrer, 33.1 g of 3-trimethoxypropylsuccinic anhydride (manufactured by Shin-Etsu Chemical Co., Ltd., trade name X-12-967C) was added as a carboxylic acid-based silane coupling agent (a), and the liquid temperature was then maintained at 80°C for 2 hours. (C) Step: The water-dispersed silica sol was evaporated and distilled off at a reduced pressure of 170 to 110 Torr and a bath temperature of 105 to 125°C using a rotary evaporator, while DMAC (dimethylacetamide) was added, and the dispersion medium of the sol was replaced with DMAC to obtain a DMAC-dispersed silica sol (silica concentration 29.8% by mass, water 2.0% by mass) treated with 3-trimethoxypropylsuccinic anhydride. (D) Step: Next, while stirring the DMAC-dispersed silica sol with a magnetic stirrer, 25.0 g of phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-103) was added as a non-carboxylic acid silane coupling agent (b), and the liquid temperature was maintained at 80°C for 2 hours. Thereafter, the solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 150 to 110 Torr and a bath temperature of 105 to 125°C, thereby obtaining a DMAC-dispersed silica sol (silica concentration 30.7% by mass, pH 4.2, viscosity (20°C) 5 mPa s (7 mPa s), water 0.1% by mass, particle size measured by dynamic light scattering method 13 nm, average primary particle size 12 nm).

[0080] Example 2 The same operation as in Example 1 was performed, except that in step (B) of Example 1, the amount of 3-trimethoxypropylsuccinic anhydride added as the carboxylic acid silane coupling agent (a) was changed to 16.5 g, to obtain a DMAC-dispersed silica sol (silica concentration 30.8 mass %, pH 4.4, viscosity (20°C) 4 mPa s (6 mPa s), water 0.1 mass %, particle size measured by dynamic light scattering method 13 nm, average primary particle size 12 nm).

[0081] Example 3 The same operation as in Example 1 was performed, except that in step (B) of Example 1, the amount of 3-trimethoxypropylsuccinic anhydride added as the carboxylic acid silane coupling agent (a) was changed to 8.3 g, to obtain a DMAC-dispersed silica sol (silica concentration 30.8 mass %, pH 4.6, viscosity (20°C) 4 mPa s (6 mPa s), water 0.1 mass %, particle size measured by dynamic light scattering method 14 nm, average primary particle size 12 nm).

[0082] Example 4 The same operation as in Example 1 was carried out, except that in step (D) of Example 1, the non-carboxylic acid-based silane coupling agent (b) was changed to 17.2 g of methyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name KBM-13), to obtain a DMAC-dispersed silica sol (silica concentration 30.8 mass%, pH 4.2, viscosity (20°C) 4 mPa s (6 mPa s), water 0.2 mass%, particle size by dynamic light scattering method 13 nm, average primary particle size 12 nm).

[0083] Example 5 The same operation as in Example 1 was carried out, except that in step (D) of Example 1, the non-carboxylic acid-based silane coupling agent (b) was changed to 31.3 g of 3-methacryloxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name KBM-503), to obtain a DMAC-dispersed silica sol (silica concentration 30.6 mass%, pH 4.3, viscosity (20°C) 4 mPa s (6 mPa s), water 0.3 mass%, particle size by dynamic light scattering method 13 nm, average primary particle size 12 nm).

[0084] Example 6 The same operation as in Example 1 was performed, except that the raw material in step (A) of Example 1 was changed to water-dispersed silica sol ST-OL (average primary particle size 45 nm, pH 2.8, silica concentration 20 mass%, manufactured by Nissan Chemical Industries, Ltd.), to obtain a DMAC-dispersed silica sol (silica concentration 30.8 mass%, pH 4.2, viscosity (20°C) 3 mPa s (6 mPa s), water 0.1 mass%, particle size by dynamic light scattering method 88 nm, average primary particle size 45 nm).

[0085] Example 7 The same operation as in Example 1 was carried out, except that in step (B) of Example 1, 3-trimethoxypropylsuccinic anhydride was used as the carboxylic acid-based silane coupling agent (a) with 21.6 g of a carboxy group-containing organosiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., product name X-12-1135), to obtain a DMAC-dispersed silica sol (silica concentration 30.8 mass %, pH 4.1, viscosity (20°C) 6 mPa s (7 mPa s), water 0.3 mass %, particle size by dynamic light scattering method 15 nm, average primary particle size 12 nm).

[0086] (Comparative Example 1) Step (A): Water-dispersed silica sol ST-O-33 (average primary particle size 12 nm, pH 3, silica concentration 33 mass%, manufactured by Nissan Chemical Industries, Ltd.) was prepared. Step (B): 1000 g of water-dispersed silica sol ST-O-33 (average primary particle size 12 nm, pH 3, silica concentration 33 mass%, manufactured by Nissan Chemical Industries, Ltd.) was charged into a 2 L recovery flask, and while stirring the sol with a magnetic stirrer, 33.1 g of 3-trimethoxypropylsuccinic anhydride was added as a carboxylic acid-based silane coupling agent (a), and the liquid temperature was then maintained at 80°C for 2 hours. Step (C): The water-dispersed silica sol was evaporated and distilled off at a reduced pressure of 170 to 110 Torr and a bath temperature of 105 to 125°C using a rotary evaporator, while DMAC (dimethylacetamide) was supplied to replace the dispersing medium of the sol with DMAC, thereby obtaining a DMAC-dispersed silica sol (silica concentration 30.8% by mass, pH 4.4, viscosity (20°C) 8 mPa s (10 mPa s), water 0.2% by mass, particle size by dynamic light scattering method 24 nm, average primary particle size 12 nm).

[0087] Comparative Example 2 The same operation as in Comparative Example 1 was performed, except that in step (B) of Comparative Example 1, the amount of 3-trimethoxypropylsuccinic anhydride added as the carboxylic acid silane coupling agent (a) was changed to 8.3 g, to obtain a DMAC-dispersed silica sol (silica concentration 30.5 mass%, pH 4.8, viscosity (20°C) 8 mPa s (10 mPa s), water 0.1 mass%, particle size measured by dynamic light scattering 30 nm, average primary particle size 12 nm).

[0088] Comparative Example 3 In step (D) of Example 1, the same operation as in Example 1 was carried out, except that the non-carboxylic acid silane coupling agent (b) was changed to 29.8 g of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name KBM-403), to obtain a DMAC-dispersed silica sol (silica concentration 30.5 mass %, pH 4.2, viscosity (20°C) 5 mPa s (7 mPa s), water 0.4 mass %, particle size measured by dynamic light scattering method 12 nm, average primary particle size 12 nm).

[0089] (Comparative Example 4) Step (A): A water-dispersed silica sol ST-O-33 (average primary particle size 12 nm, pH 3, silica concentration 33% by mass, manufactured by Nissan Chemical Industries, Ltd.) was prepared. Step (C): 1,000 g of the silica sol was placed in a 2-L recovery flask, and 500 g of DMAC (dimethylacetamide) was added. The solvent was evaporated and distilled off using a rotary evaporator at a reduced pressure of 200 to 100 Torr and a bath temperature of 85 to 125°C while DMAC was supplied, thereby replacing the sol's dispersion medium with DMAC, thereby obtaining a colorless, transparent DMAC-dispersed silica sol (silica concentration 20.5% by mass, pH 4.5, viscosity (20°C) 3 mPa s (6 mPa s), water 0.9% by mass, particle size by dynamic light scattering method 18 nm, average primary particle size 12 nm).

[0090] Synthesis Example 1 Preparation of Polyamic Acid 4,4'-Diaminodiphenyl ether (DDE), pyromellitic dianhydride (PMDA), and NMP (N-methylpyrrolidone) and DMAC (dimethylacetamide) as solvents were polymerized at a temperature of 50°C with stirring to obtain a polyamic acid (solid content 17%, viscosity at 25°C measured with an E-type viscometer of 13,640 mPa·s) corresponding to formula (6). The polyamic acid was polymerized using an equimolar ratio of 1:1 between the DDE and PMDA. The weight-average molecular weight of the obtained polyamic acid was 63,000. n in formula (6) is the number of repeating units.

[0091] The DMAC-dispersed silica sol obtained in Examples 1 to 7 and Comparative Examples 1 to 4 was added to the polyamic acid obtained in Synthesis Example 1 in a mass ratio of resin / SiO ２The components were mixed in a glass bottle so that the ratio of the silica to the total weight of the components was 85 / 15, and the mixture was degassed and stirred for 20 minutes using a vacuum degasser (manufactured by EME, trade name V-mini300) to obtain a silica-blended polyamic acid.

[0092] The resulting silica-blended polyamic acid was then applied to a Cu plate (manufactured by AS ONE Corporation, product name HC0536, 300 mm x 300 mm, 0.5 mm thick) using an applicator (manufactured by BEVS, product name: Film applicator with film thickness adjustment function B / M150 mm), followed by solvent removal and thermal curing under conditions of 70°C for 30 minutes, 100°C for 30 minutes, 150°C for 30 minutes, and 290°C for 60 minutes, thereby obtaining a Cu plate (coating thickness: 29-32 μm) with a baked silica-blended polyimide. This was then cut into 5 cm squares to serve as insulation test samples.

[0093] (Coating Film Condition Test / Coating Film Appearance and Cross Section) The coating film appearance and cross section of the insulation test sample obtained by the above method were observed visually and by SEM.

[0094] In the SEM observation, the cross section of the coating film was observed using a focused ion beam scanning electron microscope (manufactured by Thermo Fisher Scientific, trade name Helicos G3, magnification 100,000 times).

[0095] In the examples and comparative examples, if no turbidity or foaming of the coating film was visually observed in the appearance of the coating film, and no silica particle aggregates were observed in cross-sectional SEM observation, the silica particles were well dispersed in the resin and the result was rated as "OK."

[0096] Furthermore, in the examples and comparative examples, when cloudiness or foaming of the coating film was visually confirmed in the appearance of the coating film and aggregates of silica particles were confirmed by cross-sectional SEM observation, the silica particles were not dispersed in the resin and were rated as "NG."

[0097] The blank (a composition containing only polyimide resin and no silica particles) was visually inspected for the presence or absence of turbidity or bubbles in the coating film appearance, and a state in which these were not present was rated as "OK," while a state in which these were present was rated as "NG."

[0098] (Measurement of dielectric breakdown life) A plate-shaped sample measuring 50 mm x 50 mm and 0.5 mm thick was measured for dielectric breakdown life using a dielectric breakdown tester manufactured by Yamayo Testing Instruments, Model: YST-243WS, at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz. The electrodes used were a flat electrode (φ = 25 mm) at the bottom and a spherical electrode (φ = 20 mm) at the top, and the test was performed with both electrodes in contact with the sample. Three to four measurements were performed at an applied voltage of 3.0 kV, and the average value was recorded. As a blank, a sample containing only silica-free polyimide resin was used and similarly measured.

[0099] The results of the coating condition test and the measurement of the dielectric breakdown life are shown in Table 1.

[0100] The DMAC-dispersed silica sols obtained in Examples 1 to 7 were able to improve the insulation life of the cured films obtained by baking silica-blended polyimide, compared to Comparative Examples 1 to 4.

[0101] The present invention provides a silica sol in which silica particles are dispersed in a nitrogen-containing solvent to achieve good compatibility with polyimide or polyamide polar resins. It also provides an insulating resin composition containing the silica sol and a resin. Furthermore, the present invention provides an insulating coated conductor that, when used as an insulating resin composition, can maintain a long insulation life.

Claims

1. A silica sol in which silica particles are dispersed in a nitrogen-containing solvent, the silica particles having an average primary particle size of 5 to 100 nm, and at least a portion of the silica particles having a particle surface coated with a hydrolysate of a carboxylic acid-based silane coupling agent (a) and a hydrolysate of a non-carboxylic acid-based silane coupling agent (b).

2. The silica sol according to claim 1, wherein the carboxylic acid-based silane coupling agent (a) is a silane coupling agent containing a carboxyl group, an acid anhydride group, a carboxylic acid ester group, or an organic group containing any of them.

3. A silica sol according to claim 1 or 2, wherein the non-carboxylic acid silane coupling agent (b) is a silane coupling agent containing an organic group containing at least an alkyl group, a (meth)acryloyl group, or an aryl group.

4. The carboxylic acid-based silane coupling agent (a) is represented by the formula (1) and the formula (2): (In formulas (1) and (2), R １ and R ３ are each a carboxyl group, an acid anhydride group, a carboxylate group, or an organic group containing them and bonded to a silicon atom via a Si-C bond; R ２ and R ４ each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, X represents an alkylene group, an NH group, or an oxygen atom, a represents an integer of 1 to 3, b represents an integer of 1 to 2, and c represents an integer of 0 or 1. The silica sol according to any one of claims 1 to 3, 5. The non-carboxylic acid-based silane coupling agent (b) is represented by the formula (3), the formula (4), and the formula (5): (In formula (3), R ５ each represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, or a cyano group, and is bonded to a silicon atom by a Si-C bond; R ６ each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, and d represents an integer of 1 to 3. In formulas (4) and (5), R ７ and R ９ are each an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and bonded to a silicon atom by a Si—C bond, R ８ and R １０ each represents an alkoxy group, an acyloxy group, a hydroxyl group, or a halogen group, Y represents an alkylene group, an NH group, or an oxygen atom, e is an integer of 1 to 3, f is an integer of 0 or 1, and g is an integer of 1 to 3. The silica sol according to any one of claims 1 to 4, 6. The silica sol according to any one of claims 1 to 5, comprising silica particles coated with a hydrolysate of a carboxylic acid silane coupling agent (a) and a non-carboxylic acid silane coupling agent (b) in a mass ratio of 1:0.1 to 10.

7. The silica sol according to any one of claims 1 to 6, wherein the nitrogen-containing solvent is an amide solvent.

8. The silica sol according to any one of claims 1 to 7, wherein the nitrogen-containing solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or N-ethylpyrrolidone.

9. An insulating resin composition comprising the silica sol according to any one of claims 1 to 8 and a nitrogen-containing polymer.

10. The insulating resin composition according to claim 9, wherein the ratio of parts by mass of the nitrogen-containing polymer to 1 part by mass of silica contained in the silica sol is 1 to 100.

11. The insulating resin composition according to claim 9 or 10, wherein the nitrogen-containing polymer is a polyimide, a polyamide, a polyamic acid, a polyamideimide, a polyetherimide, or a polyesterimide.

12. An insulating coated conductor coated with the insulating resin composition according to any one of claims 9 to 11.

13. A polyamic acid consisting of 4,4'-diaminodiphenyl ether (DDE) and pyromellitic anhydride (PMDA) is used as a resin, and the mass ratio of resin / SiO ２ The insulating resin composition according to any one of claims 9 to 11, wherein a silica-blended polyamic acid adjusted to have a composition ratio of 1:85 / 15 is heated at 290°C on a Cu plate to obtain a silica-blended polyimide baked thereon (film thickness: 29 to 32 µm), and the insulating breakdown life at a test temperature of 155°C (in air), an applied voltage of 3.0 kV, and a frequency of 50 Hz is 50 minutes or longer.

14. A method for producing a silica sol according to any one of claims 1 to 8, comprising the following steps (A) to (D): step (A): preparing a silica sol in which silica particles having an average primary particle size of 5 to 100 nm are dispersed in an aqueous medium; step (B): adding at least one carboxylic acid silane coupling agent (a) selected from the group consisting of formulas (1) and (2) to the silica sol obtained in step (A); step (C): performing solvent replacement of the dispersion medium of the silica sol obtained in step (B) with a nitrogen-containing solvent; and step (D): adding at least one non-carboxylic acid silane coupling agent (b) selected from the group consisting of formulas (3) and (5) to the silica sol obtained in step (C).

15. A method for producing an insulating resin composition, comprising steps (E) and (F) in addition to steps (A) to (D) as recited in claim 14: step (E): a step of mixing a nitrogen-containing polymer with the silica sol obtained in step (D), in which silica particles are dispersed in a nitrogen-containing solvent; and step (F): a step of removing a part or all of the nitrogen-containing solvent from the silica sol obtained in step (E).